18F—tagged inhibitors of prostate specific membrane antigen (PSMA) and their use as imaging agents for prostate cancer

ABSTRACT

The present invention generally relates to the field of radiopharmaceuticals and their use in nuclear medicine as tracers and imaging agents for various disease states of prostate cancer.

This application is a continuation of PCT/EP2016/001573, filed Sep. 19,2016, which claims priority of EP 15002800.9, filed Sep. 30, 2015, EP16164090.9, filed Apr. 6, 2016, and EP16182764.7, filed Aug. 4, 2016.The contents of the above-identified applications are incorporatedherein by reference in their entirety.

The present invention generally relates to the field ofradiopharmaceuticals and their use in nuclear medicine as tracers andimaging agents and for the various disease states of prostate cancer.

BACKGROUND OF THE INVENTION

Prostate cancer (PCa) is the leading cancer in the US and Europeanpopulation. At least 1-2 million men in the western hemisphere sufferfrom prostate cancer and it is estimated that the disease will strikeone in six men between the ages of 55 and 85. There are more than300.000 new cases of prostate cancer diagnosed each year in USA. Themortality from the disease is second only to lung cancer. Currentlyanatomic methods, such as computed tomography (CT), magnetic resonance(MR) imaging and ultrasound, predominate for clinical imaging ofprostate cancer. An estimated $2 billion is currently spent worldwide onsurgical, radiation, drug therapy and minimally invasive treatments.However, there is presently no effective therapy for relapsing,metastatic, androgen-independent prostate cancer.

A variety of experimental low molecular weight PCa imaging agents arecurrently being pursued clinically, including radiolabeled cholineanalogs ([¹¹C]Choline, [¹⁸F]FECh, [¹⁸F] FMC,[¹⁸F]fluorodihydrotestosterone ([¹⁸F]FDHT),anti-1-amino-3-[¹⁸F]fluorocyclobutyl-1-carboxylic acid(anti[¹⁸F]F-FACBC, [¹¹C]acetate and1-(2-deoxy-2-[¹⁸F]fluoro-L-arabinofuranosyl)-5-methyluracil (-[¹⁸F]FMAU)(Scher, B.; et al. Eur J Nucl Med Mol Imaging 2007, 34, 45-53; Rinnab,L.; et al. BJU Int 2007, 100, 786,793; Reske, S. N.; et al. J Nucl Med2006, 47, 1249-1254; Zophel, K.; Kotzerke, J. Eur J Nucl Med Mol Imaging2004, 31, 756-759; Vees, H.; et al. BJU Int 2007, 99, 1415-1420; Larson,S. M.; et al. J Nucl Med 2004, 45, 366-373; Schuster, D. M.; et al. JNucl Med 2007, 48, 56-63; Tehrani, O. S.; et al. J Nucl Med 2007, 48,1436-1441). Each operates by a different mechanism and has certainadvantages, e.g., low urinary excretion for [¹¹C]choline, anddisadvantages, such as the short physical half-life of positron-emittingradionuclides.

It is well known that tumors may express unique proteins associated withtheir malignant phenotype or may over-express normal constituentproteins in greater number than normal cells. The expression of distinctproteins on the surface of tumor cells offers the opportunity todiagnose and characterize disease by probing the phenotypic identity andbiochemical composition and activity of the tumor. Radioactive moleculesthat selectively bind to specific tumor cell surface proteins provide anattractive route for imaging and treating tumors under non-invasiveconditions. A promising new series of low molecular weight imagingagents targets the prostate-specific membrane antigen (PSMA) (Mease R.C. et al. Clin Cancer Res. 2008, 14, 3036-3043; Foss, C. A.; et al. ClinCancer Res 2005, 11, 4022-4028; Pomper, M. G.; et al. Mol Imaging 2002,1, 96-101; Zhou, J.; etr al. Nat Rev Drug Discov 2005, 4, 1015-1026; WO2013/022797).

PSMA is a trans-membrane, 750 amino acid type II glycoprotein that hasabundant and restricted expression on the surface of PCa, particularlyin androgen-independent, advanced and metastatic disease (Schulke, N.;et al. Proc Natl Acad Sci USA 2003, 100, 12590-12595). The latter isimportant since almost all PCa become androgen independent over thetime. PSMA possesses the criteria of a promising target for therapy,i.e., abundant and restricted (to prostate) expression at all stages ofthe disease, presentation at the cell surface but not shed into thecirculation and association with enzymatic or signaling activity(Schulke, N.; et al. Proc. Natl. Acad. Sci. USA 2003, 100, 12590-12595).The PSMA gene is located on the short arm of chromosome 11 and functionsboth as a folate hydrolase and neuropeptidase. It has neuropeptidasefunction that is equivalent to glutamate carboxypeptidase II (GCPII),which is referred to as the “brain PSMA”, and may modulate glutamatergictransmission by cleaving N-acetylaspartylglutamate (NAAG) toN-acetylaspartate (NAA) and glutamate (Nan, F.; et al. J Med Chem 2000,43, 772-774). There are up to 10⁶ PSMA molecules per cancer cell,further suggesting it as an ideal target for imaging and therapy withradionuclide-based techniques (Tasch, J.; et al. Crit Rev Immunol 2001,21, 249-261).

The radio-immunoconjugate of the anti-PSMA monoclonal antibody (mAb)7E11, known as the PROSTASCINT® scan, is currently being used todiagnose prostate cancer metastasis and recurrence. However, this agenttends to produce images that are challenging to interpret (Lange, P. H.PROSTASCINT scan for staging prostate cancer. Urology 2001, 57, 402-406;Haseman, M. K.; et al. Cancer Biother Radiopharm 2000, 15, 131-140;Rosenthal, S. A.; et al. Tech Urol 2001, 7, 27-37). More recently,monoclonal antibodies have been developed that bind to the extracellulardomain of PSMA and have been radiolabeled and shown to accumulate inPSMA-positive prostate tumor models in animals. However, diagnosis andtumor detection using monoclonal antibodies has been limited by the lowpermeability of the monoclonal antibody in solid tumors.

The selective targeting of cancer cells with radiopharmaceuticals forimaging or therapeutic purposes is challenging. A variety ofradionuclides are known to be useful for radio-imaging or cancerradiotherapy, including ¹¹C, ¹⁸F, ¹¹¹In, ⁹⁰Y, ⁶⁸Ga, ¹⁷⁷Lu, ^(99m)Tc,¹²³I and ¹³¹I Recently it has been shown that some compounds containinga glutamate-urea-glutamate (GUG) or a glutamate-urea-lysine (GUL)recognition element linked to a radionuclide-ligand conjugate exhibithigh affinity for PSMA.

Several ¹⁸F-tagged compounds which show PSMA interaction and aresuitable for the detection of prostate cancer are shown in EP 14 003570.0. These compounds, however, show high lipophilic properties whichmake them, to a certain extent, difficult to handle and to administer.

New agents that will enable rapid visualization of prostate cancer areneeded. Thus, the object of the present invention is to develop ligandsthat interact with PSMA and carry appropriate radionuclides whichprovide a promising and novel targeting option for the detection,treatment and management of prostate cancer.

SUMMARY OF THE INVENTION

The solution of said object is achieved by providing the embodimentscharacterized in the claims.

The inventors found new compounds which are useful radiopharmaceuticalsand their use in nuclear medicine as tracers and imaging agents and forvarious disease states of prostate cancer.

The novel imaging agents with structural modifications in the linkerregion have improved tumor targeting properties and pharmacokinetics.The pharmacophore presents three carboxylic groups able to interact withthe respective side chains of PSMA and an oxygen as part of zinccomplexation in the active center. Besides these obligatoryinteractions, the inventors were able to optimize the lipophilicinteractions in the linker region in comparison to the compoundsdescribed in EP 14003570.0. Moreover, the inventors added somehydrophilic building blocks to the linkler for an enhancement of thepharmakokinetics.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: ¹⁸F-Labelling of macromolecules

FIG. 2: ¹⁸F-Fluorination via prosthetic groups

FIG. 3: ¹⁸F-prosthetic groups for peptides

FIG. 4: ¹⁸F-Labelled Prosthetic Groups using “Click Chemistry”

FIG. 5: Formation of [¹⁸F]aryltrifluoroboronates and fluoride sensors

FIG. 6: Complexes of ¹⁸F-Fluorides

FIG. 7: ¹⁸F-Labelling of RGD peptides

FIG. 8: Organ distribution of [¹⁸F]PSMA-1007 in PSMA-positive LNCaP mice(normal and blocked) and in PSMA negative PC3 mice vs. [¹⁸F]PSMA-1009([¹⁸F]DCFPyL) in PSMA positive LNCaP mice

FIG. 9: Organ distribution of [¹⁸F]PSMA-1007 in PSMA-positive LNCaP mice(non-blocked and blocked) vs. [¹⁸F]PSMA1003 in PSMA positive LNCaP mice(non-blocked)

FIG. 10: MIP of [¹⁸F]PSMA-1007 in a PSMA-positive LNCaP mouse 120-140min p.i.

FIG. 11: Time-activity curve of [¹⁸F]PSMA-1007 in a PSMA-positive LNCaPmouse, including SUV values 120-140 min p.i.

FIG. 12: Structure of PSMA-1003

FIG. 13: Structure of PSMA-1009

FIG. 14: MIPs of [¹⁸F]PSMA-1007 in a healthy volunteer

FIG. 15: Blood (black) and serum (gray) time-activity-curves expressedas percent injected dose in a healthy volunteer

FIG. 16: Time-activity-curves of normal organs with PET-delineablevolume-of-interest in a healthy volunteer

FIG. 17: Organ distribution [¹⁸F]PSMA-1007 in ten patients sufferingfrom prostate cancer expressed as SUV_(max)

FIG. 18: Tumor-to-Background ratios of [¹⁸F]PSMA-1007 in ten patientssuffering from prostate cancer calculated from the respective SUV_(max)values

FIG. 19: MIP of a 77-year old prostate cancer patient (PSA 40 ng/ml)scanned with [¹⁸F]PSMA-1007 1 and 3 h p.i. showing a large tumor mass onthe mid and apex area of prostate and several lymph node metastases.Outside of the pelvic region there was no metastasis found

FIG. 20: MIP of a 72-year old patient (PSA 15 ng/ml) diagnosed withGleason 9 (5+4) prostate cancer scanned with [¹⁸F]PSMA-1007 1 and 3 hp.i. Patient presents a large tumor mass in the whole prostate glandwith infiltration in the left seminal vesicles and several lymph nodesin the pelvic region. Two metastatic lymph nodes are located outside thepelvic region, both paraaortic at level L3/4 and L5.

FIG. 21: Transaxial PET/CT-scan of a patient (a,b) and correspondinghistopathology of the subsequent prostatectomy specimen; H&E staining(c); PSMA-immunostaining with outlined tumor contours circumscribed bythe broken line (d).

FIG. 22: Structure of preferred compounds of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to radiopharmaceuticals and their use innuclear medicine as tracers and imaging agents for the various diseasestates of prostate cancer.

Thus, the present invention concerns compounds that are represented bythe general

Formula I

with:

i, j 0, 1 m 1-5 n 0-3 R H, CH₃ AS Natural or non-natural amino acid Z:—CO₂H, —SO₂H, —SO₃H, —SO₄H, —PO₂H, —PO₃H, —PO₄H₂ X: Naphthyl, Phenyl,Biphenyl, Indolyl (═2,3-benzopyrrolyl), Benzothiazolyl, Quinoyl Y: Aryl,Alkylaryl, Cyclopentyl, Cyclohexyl, Cycloheptyl, N-Piperidyl andN-methylated Piperidyl salt ¹⁸F-Tag:

With: x = 1-5 Carboydrate:

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

If not stated otherwise, in the present invention the term “alkyl” byitself or as part of another molecule, means a straight or branchedchain, or cyclic hydrocarbon radical, or combination thereof, which maybe fully saturated, mono- or polyunsaturated and can include di- andmultivalent radicals, The “alkyl” residue is preferably C₁ to C₁₀ andmay be unsubstituted or substituted (e.g with halogen). Preferred alkylresidues are methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl,n-pentyl, n-hexyl, n-hepyl or n-octyl or the like. The same also appliesto the corresponding cycloalkyl compounds having preferably 3 to 10carbon atoms, e.g. cycloproyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl, cyclooctyl, etc. An unsaturated alkyl group is one havingone or more double bonds or triple bonds. Examples of unsaturated alkylgroups include, but are not limited to, vinyl, 2-propenyl, crotyl,2-isopentenyl, 2-(butadienyl), 2,4-pentadienyl, 3-(1,4-pentadienyl),ethynyl, 1- and 3-propynyl, 3-butynyl, and the higher homologs andisomers. The term “alkyl,” unless otherwise noted, is also meant toinclude those derivatives of alkyl, such as “heteroalkyl”, “haloalkyl”and “homoalkyl”.

The term “aryl”, as used herein, refers to a closed ring structure whichhas at least one ring having a conjugated pi electron system andincludes both carbocyclic aryl and heterocyclic aryl (or “heteroaryl” or“heteroaromatic”) groups. The carbocyclic or heterocyclic aromatic groupmay contain from 5 to 20 ring atoms. The term includes monocyclic ringslinked covalently or fused-ring polycyclic (i.e., rings which shareadjacent pairs of carbon atoms) groups. An aromatic group can beunsubstituted or substituted. Non-limiting examples of “aromatic” or“aryl”, groups include phenyl, 1-naphthyl, 2-naphthyl, 2-biphenyl,3-biphenyl, 4-biphenyl, anthracenyl, and phenanthracenyl. Substituentsfor each of the above noted aryl and heteroaryl ring systems areselected from the group of acceptable substituents (e.g. alkyl,carbonyl, carboxyl or halogen) described herein. The term “aryl” whenused in combination with other terms (including but not limited to,aryloxy, arylthioxy, aralkyl) includes both aryl and heteroaryl rings.Thus, the term “aralkyl” or “alkaryl” is meant to include those radicalsin which an aryl group is attached to an alkyl group (including but notlimited to, benzyl, phenethyl, pyridylmethyl and the like) includingthose alkyl groups in which a carbon atom (including but not limited to,a methylene group) has been replaced by a heteroatom, by way of exampleonly, by an oxygen atom. Examples of such aryl groups include, but arenot limited to, phenoxymethyl, 2-pyridyloxymethyl,3-(1-naphthyloxy)propyl, and the like.

“Heteroaryl” refers to aryl groups which contain at least one heteroatomselected from N, O, and S; wherein the nitrogen and sulfur atoms may beoptionally oxidized, and the nitrogen atom(s) may be optionallyquaternized. Heteroaryl groups may be substituted or unsubstituted. Aheteroaryl group may be attached to the remainder of the moleculethrough a heteroatom. Non-limiting examples of suitable groups include1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 3-pyrazolyl, 2-imidazolyl,4-imidazolyl, pyrazinyl, 2-oxazolyl, 4-oxazolyl, 2-phenyl-4-oxazolyl,5-oxazolyl, 3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 2-thiazolyl,4-thiazolyl, 5-thiazolyl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl,2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrimidyl, 4-pyrimidyl,4-benzothiazolyl, 5-benzothiazolyl, 6-benzothiazolyl, 7-benzothiazolyl,purinyl, 2-benzimidazolyl, 4-indolyl, 5-indolyl, 6-indolyl, 7-indolyl,1-isoquinolyl, 5-isoquinolyl, 2-quinoxalinyl, 5-quinoxalinyl,2-quinolyl, 3-quinolyl, 4-quinolyl, 5-quinolyl, 6-quinolyl, 7-quinolylor 8-quinolyl.

The term “amino acid” refers to naturally occurring and non-naturalamino acids, as well as amino acid analogs and amino acid mimetics thatfunction in a manner similar to the naturally occurring amino acids.Naturally amino acids are the 20 common amino acids in their D- orL-form (alanine, arginine, asparagine, aspartic acid, cysteine,glutamine, glutamic acid, glycine, histidine, isoleucine, leucine,lysine, methionine, phenylalanine, proline, serine, threonine,tryptophan, tyrosine, and valine) and pyrolysine and selenocysteine.Amino acid analogs refers to compounds that have the same basic chemicalstructure as a naturally occurring amino acid, by way of example only,an ex-carbon that is bound to a hydrogen, a carboxyl group, an aminogroup, and an R group. Such analogs may have modified R groups (by wayof example, norleucine) or may have modified peptide backbones, whilestill retaining the same basic chemical structure as a naturallyoccurring amino acid. Non-limiting examples of amino acid analogsinclude homoserine, norleucine, methionine sulfoxide, methionine methylsulfonium. Amino acids may be referred to herein by either their name,their commonly known three letter symbols or by the one-letter symbolsrecommended by the IUPAC-IUB Biochemical Nomenclature Commission. A“non-natural amino acid” refers to an amino acid that is not one of the20 common amino acids or pyrolysine or selenocysteine. Other terms thatmay be used synonymously with the term “non-natural amino acid” is“non-naturally encoded amino acid,” “unnatural amino acid,”“non-naturally-occurring amino acid” or “artificial amino acid. The term“non-natural amino acid” includes, but is not limited to, amino acidswhich occur by modification of a naturally encoded amino acid in theirbackbone or side chains. In some embodiments the non-natural amino acidcomprises a carbonyl group, an acetyl group, an aminooxy group, ahydrazine group, a hydrazide group, a semicarbazide group, an azidegroup or an alkyne group. In a preferred embodiment the non-naturalamino acid has the formula

and R′═H, CO₂H, CH₂CO₂H, C₂H₄CO₂H, CH(CO₂H)₂, CH(CH₂CO₂H)₂,CH(CO₂H)(CH₂CO₂H), CH₂CH(CO₂H)₂, SO₃H; o=1-3; R═H, CH₃

Preferred are those amino acids which bring a hydrophilic element intothe compound of Formula I.

Some of the residues herein (including, but not limited to non-naturalamino acids), may exist in several tautomeric forms. All such tautomericforms are considered as part of the compounds described herein. Also,for example all enol-keto forms of any compounds herein are consideredas part of the compositions described herein.

The linker B, i.e. the natural amino acids and/or non-naturallyoccurring amino acids, may be bound within the molecule via a peptide oramide linkage. In case of acidic amino acids (e.g. glutamic acid,aspartic acid) however, the binding may be alternatively via the α-, βor γ-position.

Although it is preferred that the Z-Group is —CO₂H it may be easilyreplaced with biosteric replacements such as —SO₂H, —SO₃H, —SO₄H, —PO₂H,—PO₃H, —PO₄H₂, see e.g. “The Practice of Medicinal Chemistry” (AcademicPress New York, 1996), page 203.

Within the meaning of the invention, all residues are consideredcombinable unless stated otherwise in the definition of the residues.All conceivable subgroupings thereof are considered to be disclosed.

The ¹⁸F-Tags of the above Table comprising triazoles exist in twoisomeric forms which belong both to the invention and are illustrated bythe given formulas.

Thus, preferred molecules of the present invention consist of threeprinciple components (as shown in FIG. 22): the hydrophilic PSMA bindingmotif (Glu-Urea-Lys=Glu-NH—CO—NH-Lys), two variable linkers (Linker Aand Linker B) and the ¹⁸F-Tag.

Some preferred lipophilic linkers (linker A) are shown below, whereinR¹=Glu-urea-Lys (PSMA binding motif) and R²=(Linker B)_(m)-[¹⁸F-Tag]with m=1-5,

The different preferred building blocks for hydrophilic linkers (linkerB) are shown below with their preferred connectivity exemplified on thebasis of the respective single amino acids (m=1 in the genericstructure)

The preferred hydrophilic linkers may also be formed from two or morebuilding blocks (m=2-5 in the generic formula), preferably selected fromthe acidic building blocks listed above. Preferred are 1-3 buildingblocks.

A number of preferred structures are listed in the table below:

I.ipophilic Hydrophilic Linker I.inker (=Linker B) Number (=Linker A)Pos. 1 Pos.2 Pos. 3 ¹⁸F-Tag 1 (2-Nal)-(Bn) (Glu) (Glu) — [¹⁸F]FN 2(2-Nal) (Glu) (Glu) — [¹⁸F]FN 3 (2-Nal) (γGlu) (Glu) — [¹⁸F]FN 4(2-Nal)-(Bn) (Glu) — — [¹⁸F]FN 5 (2-Nal)-(AcAMP) (γGlu) (γGlu) — [¹⁸F]FN6 (2-Nal)-(Bn) (Glu) (γGlu) — [¹⁸F]FN 7 (2-Nal)-(Bn) (γGlu) (Glu) —[¹⁸F]FN 8 (2-Nal)-(Bn) (γGlu) (γGlu) — [¹⁸F]FN 9 (2-Nal)-(Bn) (Asp)(Glu) — [¹⁸F]FN 10 (2-Nal)-(Bn) (βAsp) (Glu) — [¹⁸F]FN 11 (2-Nal)-(Bn)(Asp) (γGlu) — [¹⁸F]FN 12 (2-Nal)-(Bn) (βAsp) (γGlu) — [¹⁸F]FN 13(2-Nal)-(Bn) (Mal) (Glu) — [¹⁸F]FN 14 (2-Nal)-(Bn) (Mal) (γGlu) —[¹⁸F]FN 15 (2-Nal)-(Bn) (Gla) (Glu) — [¹⁸F]FN 16 (2-Nal)-(Bn) (γGla)(Glu) — [¹⁸F]FN 17 (2-Nal)-(Bn) (Gla) (γGlu) — [¹⁸F]FN 18 (2-Nal)-(Bn)(γGla) (γGlu) — [¹⁸F]FN

The structures of the preferred compounds 1-18 as exemplified in thetable above are shown below:

or

As may be understood by a person skilled in the art, the above mentionedpreferred compounds 1-18 and 1a-18a are not limited to the ¹⁸F-Tags asshown but the ¹⁸F-Tags are easily interchangeable by standard techniquesand any of the ¹⁸F-Tags exemplified in connection with Formula I may beused instead.

The invention also relates to precursors or pharmaceutically acceptablesalts of the compounds of general formula I. The invention also relatesto solvates of the compounds, including the salts as well as the activemetabolites thereof and, where appropriate, the tautomers thereofaccording to general formula I including prodrug formulations.

A “pharmaceutically acceptable salt” is a pharmaceutically acceptable,organic or inorganic acid or base salt of a compound of the invention.Representative pharmaceutically acceptable salts include, e.g., alkalimetal salts, alkali earth salts, ammonium salts, water-soluble andwater-insoluble salts, such as the acetate, carbonate, chloride,gluconate, glutamate, lactate, laurate, malate or tartrate.

The term “prodrug” refers to a precursor of a drug that is a compoundwhich upon administration to a patient, must undergo conversion bymetabolic processes before becoming an active pharmacological agent.Prodrugs are generally drug precursors that, following administration toa subject and subsequent absorption, are converted to an active, or amore active species via some process, such as conversion by a metabolicpathway. Some prodrugs have a chemical group present on the prodrug thatrenders it less active and/or confers solubility or some other propertyto the drug. Once the chemical group has been cleaved and/or modifiedfrom the prodrug the active drug is generated. Prodrugs are convertedinto active drug within the body through enzymatic or non-enzymaticreactions. Prodrugs may provide improved physiochemical properties suchas better solubility, enhanced delivery characteristics, such asspecifically targeting a particular cell, tissue, organ or ligand, andimproved therapeutic value of the drug.

Illustrative prodrugs of compounds in accordance with general formula Iare esters and amides, preferably alkyl esters of fatty acid esters.Prodrug formulations here comprise all substances which are formed bysimple transformation including hydrolysis, oxidation or reductioneither enzymatically, metabolically or in any other way. A suitableprodrug contains e.g. a substance of general formula I bound via anenzymatically cleavable linker (e.g. carbamate, phosphate, N-glycosideor a disulfide group) to a dissolution-improving substance (e.g.tetraethylene glycol, saccharides, formic acids or glucuronic acid,etc.). Such a prodrug of a compound according to the invention can beapplied to a patient, and this prodrug can be transformed into asubstance of general formula I so as to obtain the desiredpharmacological effect.

Some compounds of general formula I are encompassed in form of theracemates, their enantiomers and optionally in form of theirdiastereomers and all possible mixtures thereof.

According to the invention all chiral C-atoms shall have D- and/orL-configuration; also combinations within one compound shall bepossible, i.e. some of the chiral C-atoms may be D- and others may beL-configuration.

The obtained compounds can be optionally separated by known methods(e.g. Allinger, N. L. and Elliel E. L. in “Topics in Stereochemistry”Vol. 6, Wiley Interscience, 1971) in their enantiomers and/ordiastereomers. One possible method of enantiomeric separation is the useof chromatography.

The invention encompasses also precursors of the compounds of generalformula I. The term “precursor” refers to any compound which can be usedto produce the compounds of Formula I. An exemplary precursor may be acompound having no ¹⁸F-tag which is added at a later stage to providethe complete compound.

The invention also relates to pharmaceutical preparations which containa diagnostically or therapeutically effective amount of the activeingredients (compound according to the invention of formula I) togetherwith organic or inorganic solid or liquid, pharmaceutically acceptablecarriers which are suited for the intended administration and whichinteract with the active ingredients without drawbacks.

The phrase “pharmaceutically acceptable” is employed herein to refer tothose compounds, material, compositions, and/or dosage forms which are,within the scope of sound medical judgment, suitable for use in contactwith the tissues of a patient without excessive toxicity, irritation,allergic response, or other problem or complication, commensurate with areasonable benefit/risk ratio.

A “patient” includes an animal, such as a human, monkey, cow, horse, cator dog. The animal can be a mammal such as a non-primate and a primate(e.g., monkey and human). In one embodiment, a patient is a human being.

In general, the formula I compound or pharmaceutical compositionsthereof, may be administered orally or via a parenteral route, usuallyinjection or infusion.

A “parenteral administration route” means modes of administration otherthan enteral and topical administration, usually by injection, andincludes, without limitation, intravenous, intramuscular, intraarterial,intrathecal, intracapsular, intraorbital, intracardiac, intradermal,intraperitoneal, transtracheal, subcutaneous, subcuticular,intraarticluare, subcapsular, subarachnoid, intraspinal and intrasternalinjection and infusion.

The dosage of the compounds according to the invention is determined bythe physician on the basis of the patient-specific parameters, such asage, weight, sex, severity of the disease, etc. Corresponding to thekind of administration, the medicament is suitably formulated, e.g. inthe form of solutions or suspensions, simple tablets or dragees, hard orsoft gelatine capsules, suppositories, ovules, preparations forinjection, which are prepared according to common galenic methods.

The compounds according to the invention can be formulated, whereappropriate, together with further active substances and with excipientsand carriers common in pharmaceutical compositions, e.g.—depending onthe preparation to be produced—talcum, gum arabic, lactose, starch,magnesium stearate, cocoa butter, aqueous and non-aqueous carriers,fatty bodies of animal or vegetable origin, paraffin derivatives,glycols (in particular polyethylene glycol), various plasticizers,dispersants or emulsifiers, pharmaceutically compatible gases (e.g. air,oxygen, carbon dioxide, etc.), preservatives. In order to produce liquidpreparations, additives, such as sodium chloride solution, ethanol,sorbitol, glycerine, olive oil, almond oil, propylene glycol or ethyleneglycol, can be used.

When solutions for infusion or injection are used, they are preferablyaqueous solutions or suspensions, it being possible to produce themprior to use, e.g. from lyophilized preparations which contain theactive substance as such or together with a carrier, such as mannitol,lactose, glucose, albumin and the like. The ready made solutions aresterilized and, where appropriate, mixed with excipients, e.g. withpreservatives, stabilizers, emulsifiers, solubilizers, buffers and/orsalts for regulating the osmotic pressure. The sterilization can beobtained by sterile filtration using filters having a small pore sizeaccording to which the composition can be lyophilized, whereappropriate. Small amounts of antibiotics can also be added to ensurethe maintenance of sterility.

The phrases “effective amount” or “therapeutically-effective amount” asused herein means that amount of a compound, material, or compositioncomprising a compound of the invention, or other active ingredient whichis effective for producing some desired therapeutic effect in at least asub-population of cells in an animal at a reasonable benefit/risk ratioapplicable to any medical treatment. A therapeutically effective amountwith respect to a compound of the invention means that amount oftherapeutic agent alone, or in combination with other therapies, thatprovides a therapeutic benefit in the treatment of prevention of adisease. Used in connection with a compound of the invention, the termcan encompass an amount that improves overall therapy, reduces or avoidssymptoms or causes of disease, or enhances the therapeutic efficacy ofor synergies with another therapeutic agent.

As used herein, the terms “treating” or “treatment” is intended toencompass also diagnosis, prophylaxis, prevention, therapy and cure.

The terms “prevent”, “preventing,” and “prevention” refer to theprevention of the onset, recurrence, or spread of the disease in apatient resulting from the administration of a prophylactic ortherapeutic agent.

As noted above, compounds according general formula I are suitable foruse as radio-imaging agents or as therapeutics for the treatment ofrapidly proliferating cells, for example, PSMA expressing prostatecancer cells. According to the present invention they are called“radiopharmaceuticals”.

Preferred imaging methods are positron emission tomography (PET) orsingle photon emission computed tomography (SPECT).

Accordingly, in one embodiment, a pharmaceutical composition is providedincluding a compound of formula I, a salt, solvate, stereoisomer, ortautomer thereof, and a pharmaceutically acceptable carrier.Accordingly, a pharmaceutical composition is provided, which is suitablefor in vivo imaging and radiotherapy. Suitable pharmaceuticalcompositions may contain the compound of formula I in an amountsufficient for imaging, together with a pharmaceutically acceptableradiological vehicle. The radiological vehicle should be suitable forinjection or aspiration, such as human serum albumin; aqueous buffersolutions, e.g., tris(hydromethyl) aminomethane (and its salts),phosphate, citrate, bicarbonate, etc; sterile water physiologicalsaline; and balanced ionic solutions containing chloride and ordicarbonate salts or normal blood plasma cautions such as calciumpotassium, sodium and magnesium.

The concentration of the imaging agent or the therapeutic agent in theradiological vehicle should be sufficient to provide satisfactoryimaging. For example, when using an aqueous solution, the dosage isabout 1.0 to 100 millicuries. The actual dose administered to a patientfor imaging or therapeutic purposes, however, is determined by thephysician administering treatment. The imaging agent or therapeuticagent should be administered so as to remain in the patient for about 1hour to 10 days, although both longer and shorter time periods areacceptable. Therefore, convenient ampoules/vials containing 1 to 10 mLof aqueous solution may be prepared.

Imaging may be carried out in the normal manner, for example byinjecting a sufficient amount of the imaging composition to provideadequate imaging and then scanning with a suitable imaging or scanningmachine, such as a tomograph or gamma camera. In certain embodiments, amethod of imaging a region in a patient includes the steps of: (i)administering to a patient a diagnostically effective amount of acompound labeled with a radionuclide; exposing a region of the patientto the scanning device; and (ii) obtaining an image of the region of thepatient.

The amount of the compound of the present invention, or its salt,solvate, stereoisomer, or tautomer that is administered to a patientdepends on several physiological factors that are routinely used by thephysician, including the nature of imaging to be carried out, tissue tobe targeted for imaging or therapy and the body weight and medicalhistory of the patient to be imaged or treated using aradiopharmaceutical.

Specifically, the cell proliferative disease or disorder to be treatedor imaged using a compound, pharmaceutical composition orradiopharmaceutical in accordance with this invention is a cancer, forexample, prostate cancer and/or prostate cancer metastasis in e.g. lung,liver, kidney, bones, brain, spinal cord, bladder, etc.

The synthesis of the compounds of the present invention is carried outaccording to methods well known in the prior art (e.g. Hugenberg et al.,J. Med. Chem. 2013, 56, pp. 6858-6870). General methods for¹⁸F-labelling of various macromolecules are shown in FIG. 1-7. Inaddition, reference is made to Schubiger et al., PET Chemistry: TheDriving Force in Molecular Imaging, Ernst Schering Research Foundation,Workshop 62, Springer Verlag, ISSN 0947-6075; Ross et al., CurrentRadiopharmaceuticals, 2010, 3, 202-223; Kühnast et al., CurrentRadiopharm 3, 2010, 174; Bernard-Gauthier et al., BioMed ResearchInternational, 2014, 1; Maschauer and Prante, BioMed ResearchInternational, 2014, 1; Olberg et al., J. Med. Chem., 2010, 53, 1732;Rostovtsev et al., Angew. Chem., 2002, 114, 2708; Smith and Greaney,Org. Lett., 2013, 15, 4826. Thus, a person skilled in the art would beable to choose the right ¹⁸F-labelling depending on the startingmolecule. The synthesis of the specific linker molecules is shown in EP13004991 to which reference is made.

The synthesized compounds are chemically characterized by RP-HPLC, MS,and/or NMR.

The novel ¹⁸F-tagged imaging agents with structural modifications in thelinker region have improved tumor targeting properties andpharmacokinetics. The pharmacophore presents three carboxylic group ableto interact with the respective side chains of PSMA and an oxygen aspart of zinc complexation in the active center. Besides these obligatoryinteractions, the inventors were able to optimize the lipophilicinteractions in the linker region compared to the compounds as describedin EP 14003570.0. Further hydrophilic building blocks have been added tothe linker of the compounds of the present invention (linker B), leadingto another enhancement of the pharmacokinetics. Those compounds wereevaluated in in vitro assays (affinity, internalization) and in vivoexperiments (pPET screening and organ distribution).

Four preferred compounds with particularly promising results are¹⁸F-PSMA1007, ¹⁸F-PSMA1011, ¹⁸F-PSMA 1012 and ¹⁸F-PSMA 1015:

All compounds were labelled with fluorine-18 via 2-[¹⁸F]fluoronicotinicacid TFP ester in good radiochemical yields. Table A shows that thebinding affinity of the PSMA inhibitors prepared so far are essentiallythe same and in the typical range. Further, all compounds werespecifically internalized at 37° C. with rather high cell uptake andinternalization values (Table B). Thus, the compounds investigatedexhibit optimal in vitro characteristics for a high contrast PETimaging.

The compounds of the present invention were investigated in organdistribution studies in mice carrying a LNCaP tumor (PSMA positive) withand without PMPA block. The results which have been obtained exemplarywith PSMA1007 (this does not mean that the invention is limited in anyway to this specific compound only) are summarised in the FIGS. 8 and 9.The tumor uptake was about 8.0±2.4% ID/g. Since a quantitative blockingof the binding was not observed in the blocking experiment, the organdistribution experiment was repeated with mice carrying a PC3-tumor(PSMA negative; Results shown FIG. 8). Here, practically no tumor uptakewas observed. Thus, the tumor uptake is considered specifically.Additionally, compared to the organ distribution observed with thecontrol compound PSMA-1003 which has been described in EP 14 003 570.0and is shown in FIG. 12, the novel compound PSMA-1007 showed asignificantly reduced uptake in non-target tissue such as the liver andthe small intestine. Thus, PSMA-1007 was further evaluated in microPETexperiment. The results are shown in FIGS. 10 and 11. The LNCaP tumorwas clearly visualised in this experiment (SUV_(max)=3.1 at 120-140 minp.i.). The undesired uptake in the gallbladder may be an indicator formetabolites. Overall the novel class of fluorine-18 labelled PSMAinhibitors showed a great potential as possible tracer for the detectionof prostate cancer and its metastases.

By the application of [¹⁸F]PSMA-1007 to a healthy volunteer severalimportant insights were gained. First, the effective dose of a PET/CTscan with 200-250 MBq is with 4.3-5.4 mSv (2.15 mSv/MBq; FIG. 14). Morethan 95% of the blood pool activity is found in the serum (no ornegligible infiltration of red blood cells) and more than 90% clearancefrom the blood pool within the first 3 h after injection. So far, thoseresults are comparable to other important PSMA-tracers. However, incomparison to the other known PSMA-tracers the compounds of the presentinvention, particularly [¹⁸F]PSMA-1007, provide a very uniquehepatobiliary clearance with very small clearance via the renal pathway.This outstanding low urinary clearance enables an excellent assessmentof the prostatic bed. Thus, the tracers according to the presentinvention are perfectly suited for the primary diagnosis of prostatecancer and local recurrence.

This was further demonstrated by the results of the first-in-man study.Here, excellent tumor-to-background ratios of up to 10 were observed inthe primary tumor without any interference from tracer accumulation inthe bladder. Further, lymph node metastases with a diameter of down to 1mm could be detected, which is in the range of the resolution ofPET-Scans with F-18. Correlation with the samples gained by pelviclymphadenectomy analysis revealed a specificity of 95%. Moreover, thesamples gained from the prostatectomy were analyzed by histopathologyrevealing a nearly perfect correlation with the images acquired by PET.Those results clearly demonstrate the feasibility of prostate cancerimaging with the compounds of the present invention, particularly with[¹⁸F]PSMA-1007.

The below example explains the invention in more detail but are notconstrued to limit the invention in any way to the exemplifiedembodiments only.

EXAMPLES Example 1: Synthesis of Precursors and Cold Reference Compoundsof the ¹⁸F-Conjugated Inhibitors

The isocyanate of the glutamyl moiety was generated in situ by adding amixture of 3 mmol of bis(tert-butyl) L-glutamate hydrochloride and 1.5mL of N-ethyldiisopropylamine (DIPEA) in 200 mL of dry CH₂C₁₂ to asolution of 1 mmol triphosgene in 10 mL of dry CH₂C₁₂ at 0° C. over 4 h.After agitation of the reaction mixture for 1 h at 25° C., 0.5 mmol ofthe resin-immobilized (2-chloro-tritylresin) ε-allyloxycarbonylprotected lysine in 4 mL DCM was added and reacted for 16 h with gentleagitation. The resin was filtered off and the allyloxy-protecting groupwas removed using 30 mg tetrakis(triphenyl)palladium(0) and 400 μLmorpholine in 4 mL CH₂C₁₂ for 3 hours.

The following coupling of the “linker amino acids” (as defined inFormula I and Scheme 1 as shown above) was performed stepwise using 2mmol of the Fmoc-protected acid, 1.96 mmol of HBTU and 2 mmol ofN-ethyldiisopropylamine in a final volume of 4 mL DMF.

The product was cleaved from the resin in a 2 mL mixture consisting oftrifluoroacetic acid, triisopropylsilane, and water (95:2.5:2.5).Purification was performed using RP-HPLC and the purified product wasanalysed by analytical RP-HPLC and MALDI-MS.

For the preparation of the non-radioactive reference compounds 50 mg ofHBTU/DIPEA (0.98 and 1 Eq.) activated 6-Fluoronicotinic-3-acid wascoupled in a final volume of 4 ml DMF and agitated for 1 h at roomtemperature and the product was the cleaved of the resin as describedabove.

In some preparations a ¹⁸F-tag reactive moieties (e.g. pent-4-ynoic acidor (Boc-aminooxy)acetic acid) were attached to the terminal amino-groupfor subsequent ¹⁸F labeling.

Example 2: Production and Activation of the [¹⁸F]Fluoride

Preparation and Activation of the [¹⁸F]Fluoride

Fluorine-18 was produced by the irradiation of ¹⁸O-enriched water with16.5 MeV protons using the ¹⁸O(p,n)¹⁸F nuclear reaction. Irradiationswere performed with the Scanditronix MC32NI cyclotron at the departmentof Radiopharmaceutical Chemistry (E030) at the German Cancer ResearchCenter Heidelberg.

After transfer of the irradiated water to an automated system (TrasisAll In One 32) the [¹⁸F]F⁻ was separated from the [¹⁸O]H₂O by passingthrough an previously conditioned (5 ml 1 M K₂CO₃ and 10 ml water) anionexchange cartridge (Waters Accel™ Plus QMA Cartridge light) andsubsequently eluted with a mixture of 800 μl acetonitrile and 150 μltetrabutylammonium bicarbonate solution (320 mM in water). The mixturewas evaporated to dryness an a temperature of 100° C. under a stream ofnitrogen. This distillation was subsequently repeated two times by theadding 1.8 ml of acetonitrile for each step. After applying maximumachievable vacuum to the residue for 5 minutes at 100° C. and subsequentcooling to 50° C. the dry residue was dissolved in 2 ml oftert-butanol/acetonitrile (8:2) and used for the labelling reactions.

Alternatively, the system was also used with the classical Kryptofix®2.2.2/K₂CO₃ activation system (20 mg 2.2.2+28 μl 1 M K₂CO₃) inacetonitrile. Further, the solvent for dissolving the activated [¹⁸F]F⁻was changed to dry DMF, DMSO or acetonitrile for some experiments.

Example 3: Radiosynthesis of 6-[¹⁸F]Fluoronicotinic AcidTetrafluorophenyl Ester ([¹⁸F]FN-TFP)

To 10 mgN,N,N-Trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate (prepared as described by Olberg et al. J.Med. Chem., 2010, 53, 1732) 1 ml of tert-butanol/Acetonitrile (8:2)containing the dried [¹⁸F]KF-Kryptofix 2.2.2 komplex (0.1-10 GBq ¹⁸F)was added and the mixture was heated at 40° C. After 10 minutes themixture was diluted with 3 ml of water and the product loaded on apreconditioned Oasis MCX Plus Sep-Pak (Waters). The cartridge was rinsedwith 10 mL of water and the purified 6-[¹⁸F]Fluoronicotinic acidtetrafluorophenyl ester was eluted back to the reaction vessel using 2mL of water/acetonitrile (7:13). For achieving a higher activityconcentration a fractionized elution was done in some cases. Thereforethe loaded cartridge was rinsed with 500 μl of solvent, which werediscarded, and then eluted with 400-800 μl of solvent for furtherreactions. Usually more than 50% of the initial activity were elutedwith the second fraction.

Example 4: PSMA-1007

The synthesis of the precursor and the cold reference was performed asdescribed under example 1.

Radiosynthesis of [¹⁸F]PSMA-1007 200 μl of ([¹⁸F]FN-TFP) were added to50 μl of a 2 mg/ml solution of PSMA-1007-VL in DMSO. Then 50 μl ofbuffer (0.2 M phosphate buffer, pH 8.0) were added and the mixtureheated at 60° C. for 20 minutes. The products were separated bysemipreparative radio-HPLC and identified by analytical radio-HPLC andcomparison of the retention times with the respective non-radioactivereference compounds.

PSMA1007-VL (Precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Glu)-(Glu); (C₄₃H₅₃N₇O₁₅; 907.93 g/mol)particularly (Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(L-Glu)-(L-Glu)

MS (MALDI): m/z=908.7 [M+H⁺]⁺

PSMA-1007

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Glu)-(Glu)-FN; C₄₉H₅₅FN₈O₁₆; (1031g/mol) particularly (Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(L-Glu)-(L-Glu)-FN;

MS (MALDI): m/z=1032.1 [M+H]⁺

[¹⁸F]PSMA-1007

RCA: ca. 6%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 12.5 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 4.56 min (t_(dead):0.56 min)

Example 5: PSMA-1011

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1011 was performed asdescribed under example 4.

PSMA-1011-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Naphthylalanine)-(Glu)-(Glu); C₃₅H₄₆N₈O₁₄ (774.78g/mol)

MS (MALDI): m/z=775.3 [M+H⁺]⁺

PSMA-1011:

(Glu)-(Urea)-(Lys)-(2-Naphthylalanine)-(Glu)-(Glu)-FN; C₄₁H₄₈FN₇O₁₅(897.86 g/mol)

MS (MALDI): m/z=898.3 [M+H⁺]⁺

[¹⁸F]PSMA-1011:

RCA: ca. 7%

HPLC (Gradient: 5% A/95% B-50% A/50% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 5.72 min (t_(dead):0.56 min)

Example 6: PSMA-1012

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1012 was performed asdescribed under example 4.

PSMA-1012-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Naphthylalanine)-(γGlu)-(Glu); C₃₅H₄₆N₈O₁₄ (774.78g/mol)

MS (MALDI): m/z=775.0 [M+H⁺]⁺

PSMA-1012:

(Glu)-(Urea)-(Lys)-(2-Naphthylalanine)-(γGlu)-(Glu)-FN; C₄₁H₄₈FN₇O₁₅(897.86 g/mol) MS (MALDI): m/z=897.9 [M+H⁺]⁺

[¹⁸F]PSMA-1012:

RCA: ca. 4%

HPLC (Gradient: 5% A/95% B-50% A/50% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 5.61 min (t_(dead):0.56 min)

Example 7: PSMA-1015

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1015 was performed asdescribed under example 4.

PSMA-1015-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Glu); C₃₈H₄₆N₆O₁₂ (778.80 g/mol)

MS (MALDI): m/z=779.4 [M+H⁺]⁺

PSMA-1015:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Glu)-FN; C₄₄H₄₈FN₇O₁₃ (901.89 g/mol)

MS (MALDI): m/z=902.5 [M+H⁺]⁺

[¹⁸F]PSMA-1015:

RCA: ca. 7%

HPLC (Gradient: 5% A/95% B-50% A/50% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile,

Solvent B: 0.1% aqueous TFA): t_(ret): 6.48 min (t_(dead): 0.56 min)

Example 8: Synthesis of Dry [¹⁸F]FN-TFP

The radiosynthesis was performed as described under example 3 untilelution of the [¹⁸F]FN-TFP from the cartridge. After the washing thecartridge with 10 ml water (example 3) the cartridge was blown dry with20-40 ml air. Then the MCX cartridge was connected to a SepPak SodSulfdrying cartridge and the product was eluted with 2 ml of dryacetonitrile. For achieving a higher activity concentration afractionized elution was done in some cases. Therefore the loaded MCXcartridge was rinsed with 500 μl of solvent (after blowing the cartridgedry), which were discarded, and then the drying cartridge was connectedto the MCX cartridge and the product was eluted with 0.8-1.2 ml ofacetonitrile for further reactions. Usually more than 50% of the initialactivity were eluted with the second fraction.

Example 9: PSMA-1018

The synthesis of the precursor and the cold reference was performed asdescribed under example 1.

Radiosynthesis of [¹⁸F]PSMA-1018 200 μl of dry [¹⁸F]FN-TFP (example 8)were added to 50 μl of a 4 mg/ml solution of PSMA-1018-VL in DMSO. Then10 μl of DIPEA were added and the mixture heated at 60° C. for 20minutes. Then the reaction mixture was acidified by the addition of 10μl TFA, the products separated by semipreparative radio-HPLC andidentified by analytical radio-HPLC and comparison of the retentiontimes with the respective non-radioactive reference compounds.

PSMA-1018-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Glu)-(Glu)-(Glu); C₄₈H₆₀N₈O₁₈ (1037.03g/mol)

MS (MALDI): m/z=1037.6 [M+H⁺]⁺

PSMA-1018:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Glu)-(Glu)-(Glu)-FN; C₅₄H₆₂FN₉O₁₉(1160.12 g/mol)

MS (MALDI): m/z=1160.8 [M+H⁺]⁺

[¹⁸F]PSMA-1018:

RCA: ca. 20%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 3.87 min (t_(dead):0.56 min)

Example 10: PSMA-1019

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1019 was performed asdescribed under example 9.

PSMA-1019-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Chx)-(Glu)-(Glu); C₄₃H₅₉N₇O₁₅ (913.97 g/mol)

MS (MALDI): m/z=914.4 [M+H⁺]⁺

PSMA-1019:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Chx)-(Glu)-(Glu)-FN; C₄₉H₆₁FN₈O₁₆ (1037.05g/mol)

MS (MALDI): m/z=1037.7 [M+H⁺]⁺

[¹⁸F]PSMA-1019:

RCA: ca. 47%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 12.5 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 4.43 min (t_(dead):0.56 min)

Example 11: PSMA-1020

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1020 was performed asdescribed under example 9.

PSMA-1020-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(γGlu)-(Glu)-(Glu); C₄₀H₅₃N₇O₁₇ (903.89g/mol)

MS (MALDI): m/z=904.9 [M+H⁺]⁺

PSMA-1020:

(Glu)-(Urea)-(Lys)-(2-Nal)-(γGlu)-(Glu)-(Glu)-FN; C₄₆H₅₅FN₈O₁₈ (1026.97g/mol)

MS (MALDI): m/z=1027.9 [M+H⁺]⁺

[¹⁸F]PSMA-1020:

RCA: ca. 60%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 12.5 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent

B: 0.1% aqueous TFA): t_(ret): 6.48 min (t_(dead): 0.56 min)

Example 12: PSMA-1022

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1022 was performed asdescribed under example 9.

PSMA-1022-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(γGlu)-(γGlu); C₃₅H₄₆N₈O₁₄ (774.78 g/mol)

MS (MALDI): m/z=775.4 [M+H⁺]⁺

PSMA-1022:

(Glu)-(Urea)-(Lys)-(2-Nal)-(γGlu)-(γGlu)-FN; C₄₁H₄₈FN₇O₁₅ (897.86 g/mol)

MS (MALDI): m/z=898.8 [M+H⁺]⁺

[¹⁸F]PSMA-1022:

RCA: ca. 29%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 3.92 min (t_(dead):0.56 min)

Example 13: PSMA-1023

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1023 was performed asdescribed under example 9

PSMA-1023-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(D-Glu)-(D-Glu); C₄₃H₅₃N₇O₁₅ (907.93g/mol)

MS (MALDI): m/z=907.8 [M+H⁺]⁺

PSMA-1023:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(D-Glu)-(D-Glu)-FN; C₄₉H₅₅FN₈O₁₆(1031.00 g/mol)

MS (MALDI): m/z=1031.8 [M+H⁺]⁺

[¹⁸F]PSMA-1023:

RCA: ca. 24%

HPLC (Gradient: 5% A/95% B-50% A/50% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 3.87 min (t_(dead):0.56 min)

Example 14: PSMA-1024

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1024 was performed asdescribed under example 9.

PSMA-1024-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(D-Glu)-(Glu); C₄₃H₅₃N₇O₁₅ (907.93g/mol)

MS (MALDI): m/z=908.6 [M+H⁺]⁺

PSMA-1024:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(D-Glu)-(Glu)-FN; C₄₉H₅₅FN₈O₁₆ (1031.00g/mol)

MS (MALDI): m/z=1031.5 [M+H⁺]⁺

[¹⁸F]PSMA-1024:

RCA: ca. 27%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 3.85 min (t_(dead):0.56 min)

Example 15: PSMA-1025

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1025 was performed asdescribed under example 9.

PSMA-1025-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Gla); C₃₉H₄₆N₆O₁₄ (822.21 g/mol)

MS (MALDI): m/z=822.8 [M+H⁺]⁺

PSMA-1025:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Gla)-FN; C₄₉H₅₅FN₈O₁₆ (945.32 g/mol)

MS (MALDI): m/z=946.0 [M+H⁺]⁺

[¹⁸F]PSMA-1025:

RCA: ca. 24%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 12.5 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 4.51 min (t_(dead):0.56 min)

Example 16: PSMA-1026

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1026 was performed asdescribed under example 9.

PSMA-1026-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Sala); C₃₆H₄₄N₆O₁₃S (800.83 g/mol)

MS (MALDI): m/z=801.8 [M+H⁺]⁺

PSMA-1026:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Sala)-FN; C₄₂H₄₆FN₇O₁₄S (923.92 g/mol)

MS (MALDI): m/z=924.7 [M+H⁺]⁺

[¹⁸F]PSMA-1026:

RCA: ca. 57%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 12.5 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 4.03 min (t_(dead):0.56 min)

Example 17: PSMA-1027

The synthesis of the precursor and the cold reference was performed asdescribed under example 1. The synthesis [¹⁸F]PSMA-1027 was performed asdescribed under example 9.

PSMA-1027-VL (precursor):

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Sala)-(Sala); C₃₉H₄₉N₇O₁₇S₂ (951.97g/mol)

MS (MALDI): m/z=952.7 [M+H⁺]⁺

PSMA-1027:

(Glu)-(Urea)-(Lys)-(2-Nal)-(Bn)-(Sala)-(Sala)-FN; C₄₅H₅₁FN₈O₁₈S₂(1075.06 g/mol)

MS (MALDI): m/z=1075.8 [M+H⁺]⁺

[¹⁸F]PSMA-1027:

RCA: ca. 62%

HPLC (Gradient: 5% A/95% B-95% A/5% B in 10.0 min; Flow: 3 ml/min;Column: Merck Chromolith® Performance RP-18e 100-4.6 mm; Solvent A:Acetonitrile, Solvent B: 0.1% aqueous TFA): t_(ret): 3.10 min (t_(dead):0.56 min)

Example 18: Cell Culture

For binding studies and in vivo experiments LNCaP cells (metastaticlesion of human prostatic adenocarcinoma, ATCC CRL-1740) were culturedin RPMI medium supplemented with 10% fetal calf serum and Glutamax (PAA,Austria). During cell culture, cells were grown at 37° C. in anincubator with humidified air, equilibrated with 5% CO₂. The cells wereharvested using trypsin-ethylenediaminetetraacetic acid (trypsin-1.5EDTA; 0.25% trypsin, 0.02% EDTA, all from PAA, Austria) and washed withPBS.

Example 19: Cell Binding and Internalization

The competitive cell binding assay and internalization experiments wereperformed as described previously (Eder et al. Bioconjugate Chem. 2012,23 (4), 688-697). Briefly, the respective cells (10⁵ per well) wereincubated with the radioligand (⁶⁸Ga-labeled[Glu-urea-Lys(Ahx)]2-HBED-CC (Schafer et al. EJNMMI Research 2012, 2:23doi:10.1186/2191-219X-2-23))) in the presence of 12 differentconcentrations of analyte (0-5000 nM, 100 μL/well). After incubation,washing was carried out using a multiscreen vacuum manifold (Millipore,Billerica, Mass.). Cell-bound radioactivity was measured using a gammacounter (Packard Cobra II, GMI, Minnesota, USA). The 50% inhibitoryconcentration (IC₅₀) was calculated by fitting the data using anonlinear regression algorithm (GraphPad Software). Experiments wereperformed three times. Reference is made to Table A below.

To determine the specific cell uptake and internalization, 10⁵ cellswere seeded in poly-L-lysine coated 24-well cell culture plates 24 hbefore incubation. After washing, the cells were incubated with 30 nM ofthe radiolabeled compounds for 45 min at 37° C. Specific cellular uptakewas determined by competitive blocking with2-(phosphonomethyl)pentanedioic acid (500 μM final concentration, PMPA,Axxora, Loerrach, Germany). Cellular uptake was terminated by washing 3times with 1 mL of ice-cold PBS. Cells were subsequently incubated twicewith 0.5 mL glycine-HCl in PBS (50 mM, pH=2.8) for 5 min to remove thesurface-bound fraction. The cells were washed with 1 mL of ice-cold PBSand lysed using 0.3 N NaOH (0.5 mL). The surface-bound and theinternalized fractions were measured in a gamma counter. The cell uptakewas calculated as percent of the initially added radioactivity bound to10⁵ cells [% ID/10⁵ cells]. The main results are given in Table B.

TABLE A Binding Affinity Assay Compound IC₅₀ [nM] PSMA-1007 5 PSMA-10117 PSMA-1012 7 PSMA-1015 4 PSMA-1018 14 PSMA-1019 12 PSMA-1020 9PSMA-1022 8 PSMA-1023 8 PSMA-1024 8 PSMA-1025 9 PSMA-1026 14 PSMA-1027 7

TABLE B Specific Internalization Cell surface Internalised InternalizedCompound [% ID/10⁵ cells] [% ID/10⁵ cells] fraction [%]* PSMA-1007 2.76.5 71 PSMA-1011 4.1 0.7 15 PSMA-1012 6.9 2.7 28 PSMA-1015 14.3 6.0 30PSMA-1018 1.1 0.9 45 PSMA-1019 5.5 1.9 26 PSMA-1020 6.8 1.5 18 PSMA-10223.5 1.0 22 PSMA-1023 6.5 3.2 33 PSMA-1024 5.3 2.1 28 PSMA-1025 4.3 3.142 PSMA-1026 1.3 1.3 50 PSMA-1027 0.9 1.4 60 *(Internalizedactivity/total activity)*l00

Example 20: MicroPET

For the microPET studies, 10-25 MBq of the radiolabeled compounds in avolume of 0.10 ml (60 pmol) were injected via a lateral tail vein intomice bearing LNCaP tumor xenografts. The anesthetized animals (2%sevoflurane, Abbott, Wiesbaden, Germany) were placed in prone positioninto the Inveon small animal PET scanner (Siemens, Knoxville, Tenn.,USA) to perform dynamic microPET scans. The results are shown in FIGS.10 and 11.

Example 21: Plasma Binding and Stability

For the determination of the plasma binding 3 μl of 6 μmolar c.a.[¹⁸F]PSMA solution was added to 300 μl human serum AB and incubated at37° C. for 1 h. Subsequently the product mixture was analyzed bysize-exclusion chromatography.

No plasma binding was observed with any of the compounds.

For the determination of the plasma stability 50 μl of 6 μmolar c.a.[¹⁸F]PSMA solution was added to 450 μl human serum AB and incubated at37° C. At 1, 2 and 4 h samples were prepared. Therefore 100 μl of thetracer/plasma mixture were added to 100 μl of acetonitrile. Subsequentlythe mixture was centrifuged at 13000 rpm for 3 minutes. 100 μl of thesupernatant were added to 100 μl of acetonitrile, centrifuged at 13000rpm for 5 minutes, the liquid separated from any residual solids andanalyzed by HPLC.

All of the compounds were stable in human plasma at 37° C. for at least4 hours.

Example 22: In Vivo Experiments

For in vivo experiments, 8 week old BALB/c nu/nu mice weresubcutaneously inoculated into the right trunk with 5×10⁶ LNCaP- orPC3-cells in 50% Matrigel. When the size of tumor was approximately 1cm³, the radiolabeled compound was injected via the tail vein (ca. 30MBq, 60 pmol for μPET imaging; ca. 1 MBq, 60 pmol for organdistribution).

Organ Distribution

The F-18 labeled compounds were injected via tail vein (1-2 MBq permouse; 60 pmol). At 1 h after injection, the animals were sacrificed.Organs of interest were dissected, blotted dry, and weighed. Theradioactivity was measured with a gamma counter (Packard Cobra II, GMI,Minnesota, USA) and calculated as % ID/g. The main results are given inFIGS. 8 and 9.

The compounds PSMA 1003 and PSMA 1009 are for comparison and are shownin FIGS. 12 and 13.

Example 23: [¹⁸F]PSMA-1007 for Human Application

[¹⁸F]PSMA-1007 was produced by conjugation of dry [¹⁸F]FN-TFP (Example8) to PSMA1007-VL (Example 4) under dry conditions (analogously Example9) on an automated synthesis module (Trasis AllInOne) and purified bysemi-preparative HPLC. Radio-HPLC was performed to determine thechemical identity and the chemical and radiochemical purity of[¹⁸F]PSMA-1007. Residual solvents were determined by gas chromatography.The radionuclide purity was controlled by half-life measurement. Theproduct solution was tested for sterility, bacterial endotoxins(LAL-test), pH, colorlessness and particles. The integrity of thesterile filter after filtration was examined using the bubble-pointtest.

Example 24: Application of [¹⁸F]PSMA-1007 to a Healthy Volunteer

The healthy subject was injected a total activity of 300 MBq andsubsequently PET scans were performed on a Biograph mCT Flow scanner(Siemens, Erlangen, Germany) in three blocks. Block 1 contained PET-1(start 5 min p.i.) to PET-7 (ending 140 min p.i.), block 2 containedPET-8 (start 180 min p.i.) and PET-9 (240-270 min p.i.), block 3contained PET-10 (440-480 min p.i.). A non-enhanced low-dose CT(estimate 1.43 mSv, respectively) for attenuation correction wasperformed at the beginning of each block, followed by serial emissionscans without moving the volunteer in between.

Kidneys, liver, spleen, whole heart, upper and lower large intestine,parotid glands, submandibular glands and urinary bladder were segmentedinto volumes of interest (VOIs) using a percentage of maximum thresholdbetween 20% and 30% using the corresponding CT as guidance and then timeactivity curves (TACs) were calculated for all organs. The TAC for redmarrow was derived from the venous blood samples and then the dose forthe red marrow calculated (S. Shen et al., JNM 2002, 43, 1245-1253; G.Sgouros et al., JNM 1993, 34, 689-694.). The TAC for the urinary bladdercontent was a combination of estimated activity in the urinary bladderVOI in PET and activity measured in the voided urine. Curve fitting wasapplied to all TACs. Kidneys, salivary glands, upper and lower largeintestine and heart were fitted with a bi-exponential function. Forliver, spleen and urinary bladder content a mono-exponential fit to thelast three time points was performed.

Absorbed and effective dose calculations were performed using the ICRPendorsed IDAC 1.0 package which is integrated in QDOSE. Additionally,residence times of all included source organs and remainder body wereexported as an OLINDA case file for dose calculation (OLINDA 1.1). Theabsorbed doses to the salivary glands (parotid and submandibular glands)were determined using the spherical model. The organ masses for thesalivary glands were estimated with 25 g for a parotid and 12.5 g for asubmandibular gland (ICRP publication 89). The results are summarized inFIGS. 14-16.

Example 25: Application of [¹⁸F]-PSMA-1007 in a Patients Suffering fromProstate Cancer

Ten patients (age 60-80 years) suffering from a newly diagnosedhigh-risk prostate cancer with a gleason score of 7-9 and initial PSAlevels of 5-90 ng/ml were injected 100-360 MBq [¹⁸F]-PSMA-1007 andsubsequently PET scans were performed on a Biograph mCT Flow scanner(Siemens, Erlangen, Germany) at 1 and 3 h p.i. The results are depictedin FIGS. 17 and 18 as mean values of the SUV_(mean) and SUV_(max),respectively. The pictures gained with the PET scans are exemplified inFIGS. 19 and 20 as maximum intensity projections.

Eight of the patients underwent radical prostatectomy with extendedpelvic lymphadenectomy. Analyses of prostatectomy specimen wereperformed blinded to PET-data under the supervision of dedicateduropathologists, according to International Society of UrologicalPathology standards (T. H. van der Kwast et al. Mod. Phathol. 2011, 24,16-25). Representative sections were stained by immunohistochemistry.The sections were deparaffinized in xylene and rehydrated in a gradedethanol series. Antigen retrieval was performed with a steam cookerusing retrieval buffer (Target Retrieval Solution, Dako). A mousemonoclonal antibody against PSMA (clone 3E6, Dako) was used at a 1:100dilution and incubated overnight at 4° C. ad subsequentlyimmunodetection was performed using the Histostain-Plus detection kit(Invitrogen). Stained sections were scanned using a Nanozoomer 2.0-HTScansystem (Hamamatsu Photonics) to generate digital whole slide images.The staining revealed a nearly perfect correlation with the PET scan, asexemplified in FIG. 21.

The invention claimed is:
 1. A compound of Formula I:

with: i, j 0, 1 m 1-5 n 0-3 R H, CH₃ AS Natural or non-natural aminoacid Z: —CO₂H, —SO₂H, —SO₃H, —SO₄H, —PO₂H, —PO₃H, —PO₄H₂ X: Naphthyl,Phenyl, Biphenyl, Indolyl (═2,3-benzopyrrolyl), Benzothiazolyl, QuinoylY: Aryl, Alkylaryl, Cyclopentyl, Cyclohexyl, Cycloheptyl, N-Piperidyland N-methylated Piperidyl salt ¹⁸F-Tag:

With: x = 1-5 Carboydrate:

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl

R₁: Any alkyl, aryl or arylalkyl linker especially methyl, 2-ethyl,3-propyl, 2-,3-,4-phenyl, 2-,3-,4-phenylmethyl, 2-,3-,4-phenylpropyl R₂:Any alkyl or aryl group especially methyl isopropyl, tert-butyl, phenylor 1-naphtyl.


2. The compound of claim 1, wherein the non-natural amino acid has theformula

and R′═H, CO₂H, CH₂CO₂H, C₂H₄CO₂H, CH(CO₂H)₂, CH(CH₂CO₂H)₂,CH(CO₂H)(CH₂CO₂H), CH₂CH(CO₂H)₂, SO₃H; o=1-3; R═H, CH₃.
 3. Apharmaceutical composition comprising the compound of claim 1, or apharmaceutically acceptable salt or ester thereof, and apharmaceutically acceptable carrier.
 4. The compound of claim 1 havingthe structure;

wherein the linker A is selected from the group consisting of:

wherein R¹=(Glu)-(Urea)-(Lys) and R²=(Linker B)_(m)-¹⁸F Tag, m=1-5, andlinker B is selected from the group consisting of:


5. The compound of claim 1, selected from the following


6. The compound of claim 1, wherein R₁ is selected from the groupconsisting of: methyl, 2-ethyl, 3-propyl, 2-,3-,4-phenyl,2-,3-,4-phenylmethyl, and 2,3-,4-phenylpropyl.
 7. The compound of claim1, wherein R₂ is selected from the group consisting of methyl,isopropyl, tert-butyl, phenyl, and 1-naphtyl.
 8. A method of imaging aprostate region in a patient comprising the steps of: (i) administeringto a patient a diagnostically effective amount of the compound of claim1; (ii) exposing the prostate region of the patient to a scanning deviceto detect the 18F-tag; and (iii) obtaining an image of the prostateregion of the patient by the scanning device.